The present invention relates to flame-retarding of a polyketone resin useful as electrical and electronic components of office automation equipment and household appliances and housing components thereof, automobile parts and machine parts. More specifically, it relates to a flame-retarded polyketone resin composition obtained by mixing specific magnesium hydroxide particles into a polyketone resin and to molded articles thereof.
A polyketone resin is a novel resin which has been successfully synthesized from carbon monoxide and an olefin to be developed in recent years, and mechanical properties thereof fall into the category of engineering plastics. U.S. Pat. Nos. 4,843,144 and 4,880,903 disclose the production method of a linear alternating ketone terpolymer which is synthesized from an olefin such as ethylene and propylene and carbon monoxide. The thus-obtained polyketone resin is excellent in impact resistance, exhibits high impact resilience both at room temperature and at low temperatures and has excellent creep properties. However, it also has such problems that it is susceptible to a crosslinking reaction during such processes as extrusion and injection, that it has poor melt-stability and that it discolors during processing. To solve these problems, it is disclosed in Japanese Patent Laid-Open Publication No. 11-116795 that an increase in stability at the time of melt-processing and a reduction in discoloration can be accomplished by adding a stabilizer comprising a polyol and an aluminum hydroxide compound to an aliphatic ketone polymer synthesized from carbon monoxide and at least one ethylenic unsaturated hydrocarbon. In addition, the addition of an impact resistance improving agent, a flame retardant, a reinforcing filler, an antioxidant and other polymer is also disclosed therein. However, there is no detailed description of flame-retarding of this polymer in the publications.
Further, Japanese Patent Laid-Open Publication No. 11-71513 discloses a polyketone resin composition obtained by mixing 0.01 to 50 parts by weight of a liquid crystal resin, for the purpose of improving the thin-wall flowability, heat resistance, resistance to organic solvents and moldability which are useful as housing components, and 0.01 to 60 parts by weight of a flame retardant into 100 parts by weight of a polyketone resin. This publication discloses that an organic bromide, an organic phosphide, a red phosphor and the like can be used as the flame retardant and that the red phosphor may be coated with a metal hydroxide such as magnesium hydroxide. However, from the point of safety orientation at the present time, the use of the organic halogen-containing flame retardant is on its way to diminish, and the flame retardant containing phosphorus such as red phosphor is not considered satisfactory because of such problems as the generation of phosphine gas, odor and discoloration at the time of processing.
The object of the present invention is to provide a flame-retardant polyketone resin composition which does not cause damage to the working environment during the flame retarding process of a polyketone resin composition, has good moldability, retains the physical properties of the resin, and is useful as electrical and electronic components of office automation equipment and household appliances and housing components thereof, automobile parts and machine parts, all of which have an excellent appearance.
The present inventors have made various studies to solve the above problems and completed the present invention by mixing a predetermined amount of specific magnesium hydroxide particles into a polyketone resin.
The magnesium hydroxide particles used in the present invention are coated surface of magnesium hydroxide particles whose crystals grow well and which hardly agglomerate. The production method of the magnesium hydroxide particles as an additive or a flame retardant for a resin has already been known, and the magnesium hydroxide particles whose crystals grow well and which hardly agglomerate can exhibit good moldability, mechanical strength and flame retardancy. They are synthesized by the reaction between an aqueous magnesium salt such as magnesium chloride and an alkali such as caustic soda. Further, magnesium hydroxide particles obtained by the re-hydration of magnesium oxide or natural magnesium hydroxide can also be used as the flame retardant.
However, when the conventional magnesium hydroxide particles or magnesium hydroxide particles whose crystals have been fully grown for the purpose of improving the dispersibility in a resin are mixed into a polyketone, the polyketone is degraded by the heat generated at the time of molding. Since this degradation affects the mechanical properties and coloration, surface-treated magnesium hydroxide particles are used in the present invention.
According to the studies made by the present inventors, the above object of the present invention is achieved by a flame-retardant polyketone resin composition which substantially comprises (1) 40 to 85% by weight of a polyketone resin based on the total weight of the composition and (2) 15 to 60% by weight of magnesium hydroxide particles, based on the total weight of the composition, which have (a) a specific surface area measured by a BET method of 1 to 15 m2/g, (b) an average secondary particle diameter of 0.2 to 5 xcexcm, and (c) a surface coated with a surface-treating agent.
The resin composition of the present invention will be described in more detail hereinafter.
The polyketone resin used in the present invention is generally referred to as an aliphatic polyketone resin. The polyketone resin is obtained by reacting an olefin which mainly contains ethylene with carbon monoxide as described above. The polyketone resin may be one that can be used for molding and can be produced by any methods.
The polyketone resin is preferably a resin obtained by reacting an olefin mixture containing ethylene and a small portion of other olefin with carbon monoxide. The particularly preferable polyketone resin is a linear alternating ketone terpolymer in which the molar ratio (Y/X) of the following recurring units (X) and (Y) in the main chain:
(wherein D is an alkylene chain other than the ethylene chain (xe2x80x94CH2xe2x80x94CH2xe2x80x94)) is 0.01 to 0.2, preferably 0.02 to 0.1. The above recurring unit (X) is a unit based on ethylene, and the above recurring unit (Y) is a unit based on an olefin other than ethylene. The D in this Y is specifically an alkylene chain based on propylene, butylene, pentene or styrene, and the alkylene chain based on propylene is particularly preferable.
In the present invention, the magnesium hydroxide particles mixed into the above polyketone resin has a specific surface area measured by a BET method of 1 to 15 m2/g, preferably 2 to 10 m2/g. Further, the magnesium hydroxide particles have an average secondary particle diameter measured by a laser beam diffraction-scattering method of 0.2 to 5 xcexcm, preferably 0.5 to 3 xcexcm.
When the magnesium hydroxide particles having the above form are mixed into the polyketone resin in such an amount that is sufficient to impart flame retardancy to the polyketone resin, the flowability substantially lowers, the moldability deteriorates and the physical properties lower.
In the present invention, the magnesium hydroxide particles having the above form are coated with a surface-treating agent before use. When the surface-coated magnesium hydroxide particles are used, the resin composition exhibits improved flowability and excellent moldability, and the obtained molded article exhibit improved physical strength and coloring properties. As a matter of course, flame retardancy of at least V-1 is achieved on the basis of the UL94 standard, and flame retardancy of V-0 is achieved in most cases.
Illustrative examples of the surface-treating agent used for coating the surfaces of the magnesium hydroxide particles include (a) C14 to C24 higher fatty acids and alkali metal salts thereof, (b) phosphoric esters, (c) sulfuric ester salts of higher alcohols such as stearyl alcohol and oleyl alcohol, (d) silane coupling agents such as vinyl ethoxy silane, xcex3-methacryloxypropyl trimethoxysilane and xcex3-aminopropyl methoxysilane and (e) polymers such as styrene-acryl-based low-molecular-weight polymers.
As the surface-treating agent, the phosphoric esters in the above (b) has abetter effect. According to the studies of the present inventors, it has been found that the phosphoric esters represented by the following formula (1) are particularly preferable. 
(wherein R is an alkyl group having 1 to 24 carbon atoms or an alkenyl group having 2 to 24 carbon atoms, A is an alkylene group having 2 to 4 carbon atoms, n is an integer of 0 to 6, m is 1 or 2, and M is a cation which represents an alkali metal, an alkyl amine having 1 to 4 carbon atoms or an alkanol amine represented by the following formula:
(R1)3-rNxe2x80x94(Bxe2x80x94OH)r
wherein R1 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, B is an alkylene group having 2 to 4 carbon atoms, and r is an integer of 1 to 3)
Of the phosphoric esters represented by the above formula, the sodium salt of stearyl alcohol phosphoric ester is suitable.
The surface treatment is conducted as follows. The magnesium hydroxide particles dispersed in water are maintained at least at the temperature where the surface-treating agent is dissolved or emulsified, the aqueous solution of the surface-treating agent is gradually injected into the dispersion under agitation, and the resulting mixture continues to be agitated 15 to 30 minutes after the completion of the injection. The obtained slurry of the surface-treated magnesium hydroxide particles is dehydrated, washed with water and dried in accordance with the commonly used method. Further, when a compound insoluble in an aqueous solvent such as higher fatty acids is used, it is molten by heat or an organic solvent and mixed into the magnesium hydroxide powders to surface-treat the particles by a dry process using a Henschel mixer or the like. The surface-treating agent is used in an amount of 0.5 to 5% by weight, preferably 2 to 4% by weight based on the magnesium hydroxide particles.
By mixing the surface-treated magnesium hydroxide particles into a resin composition in an amount of 15 to 60% by weight, preferably 20 to 50% by weight, a polyketone resin composition which has suitable resin physical properties and undergoes little coloration can be obtained. When the content of the magnesium hydroxide particles is smaller than the above range, the flame retardancy is insufficient, while when it is larger than the above range, the flowability of the resin is poor and the moldability and mechanical strength thereof are insufficient disadvantageously.
Further, the flame-retardant resin composition of the present invention may contain other polymers in such an amount that does not impair the physical properties and appearance. For example, polyester resins, polyamide resins, polyacetals, polyethylenes, polypropylenes, ABS and polystyrenes may be contained. When these are used in combination, it is desirable to use a polyketone in which groups of one type selected from the group consisting of hydroxyl groups, carboxylic acid groups, carboxylate groups and carboxylic anhydride groups are added in the molecule or to some of the terminals. It is desirable that the total amount of these other polymers be not more than 20% by weight, preferably not more than 10% by weight, based on the resin composition of the present invention.
Further, the flame-retardant polyketone resin composition of the present invention may also contain antioxidants, age resistors, heat stabilizers, ultraviolet absorbers, light stabilizers, lubricants, mold releasing agents, colorants, pigments, crystallization nucleating agents, plasticizers and other flame retardants such as organophosphorus compounds and antimony trioxide as required.
The flame-retardant polyketone resin composition of the present invention is produced by a generally known method. For example, it can be obtained by mixing a polyketone resin, surface-treated magnesium hydroxide particles and other necessary additives together or by supplying these to separate extruders or the like and melt-kneading them at temperatures of 150xc2x0 C. to 350xc2x0 C. The mixer may be a single-screw or twin-screw extruder having a mixing unit or a kneading machine such as a kneader.